Electrophotographic photoconductors are required to have a function of maintaining a surface charge in the dark, function of generating charges upon receipt of light, and a function of transporting the charges upon receipt of light. The electrophotographic photoconductors may include so-called monolayer-type photoconductors having these functions in a single layer, or so-called function-separated laminated-layer type photoconductor having a first layer that mainly serves to generate charges upon receipt of light, and a second layer that serves to maintain the surface charge in the dark and transports charges upon receipt of light.
The above types of electrophotographic conductors are used to form images by known electrophotographic methods, such as the Carlson method. The image formation by this method may be performed by charging the photoconductor in the dark by a corona discharge, forming a desired electrostatic latent image, such as characters or drawing of an original, on the surface of the charged photoconductor, developing the thus formed electrostatic latent image by means of toner particles, transferring and fixing the toner particles representing the desired image onto a support, such as paper. After the toner transfer, remaining toner particles are removed by cleaning, and any residual electrostatic charges are removed by erase exposures, so that the photoconductor can be used again. Conventionally, a photosensitive material of the above-described electrophotographic photoconductor may be obtained by dispersing in a resin binder an inorganic photoconductive substance, such as selenium, selenium alloy, zinc oxide, or cadmium sulfide, or dispersing in a resin binder an organic photoconductive substance, such as poly-N-vinylcarbazole, 9, 10-anthracenediol polyester, hydrazone, stilbene, butadiene, benzidine, phthalocyanine, or bisazo compound, or subjecting these substances to vacuum deposition or sublimation.
Of the above-indicated organic photoconductive materials, various analyses have been made on titanyl oxyphthalocyanine. In order to enhance the stability of the photoconductive material, in particular, an alkyl diol compound having 3 to 12 carbon atoms with two hydroxy groups bonded to non-adjacent carbon atoms may be added to titanyl oxyphthalocyanine that shows the maximum peak at a Bragg angle (2.theta..+-.0.2.degree.) of 27.2.degree. in an X-ray diffraction spectrum, as disclosed in Japanese laid-open Patent Publication No. 5-313389.
As described above, titanyl oxyphthalocyanine containing such an additive as described above has been used as the photosensitive material of the electrophotographic photoconductor, as known in the art, and various studies have been conducted on improvement in the stability. The studies, however, have failed to specify or clarify a substance that is related to the characteristic of the resulting photoconductor. Namely, the relationship between the additive and electrophotographic characteristics, in particular, stability, of the photoconductor has not been made clear, though various examples of titanyl oxyphthalocyanine containing an additive have been proposed.